The latest attempt to stop the Gulf of Mexico oil leak has failed, the oil giant BP has said. BP chief operating officer Doug Suttles said the firm was now shifting to a new strategy to stop the spill. In the failed procedure - known as "top kill" - the firm had been blasting waste material into a ruptured well, after pumping heavy mud into it. The worst oil spill in US history began when a drilling rig exploded last month, killing 11 people. The thick crude has already permeated more than 70 miles (110km) of Louisiana's coastline, threatening fragile wetlands and putting the vital fishing industry at risk. New operation Mr Suttles said BP had determined that the "top kill" method - which had been going on since Wednesday - had failed after studying the results for three days. "We have not been able to stop the flow," he told reporters on Saturday. The BBC's Andy Gallacher in Louisiana says the failure is another blow for the region. BP says the next option - called the lower-marine-riser-package cap - involved an underwater robot using a saw to hack off the leaking pipe and place a cap over it. The operation is expected to last four days.